In any gun system, or more generally, projectile-firing device, conservation of momentum provides that the momentum carried by the projectile and the gases is equal to, but in the opposite direction of, the momentum imparted to the device. The momentum imparted to the device is, in turn, equal to the recoil force integrated over time, or the impulse. This is commonly referred to as the “kick” experienced when a gun is fired. While the total amount of momentum for a given projectile fired at a given velocity cannot be changed, it can be managed. The force-time profile can be changed from a very high, short-lived force to a longer, much lower amplitude force pulse.
Present recoil-mitigation devices utilize complex and expensive hydraulics, pneumatics, pistons, springs, friction, or some combination thereof. In addition, present devices are integral to the projectile-firing device and, therefore, not always easily or quickly adaptable to varying situations. Examples include U.S. Pat. No. 4,514,921 (coil spring compression), U.S. Pat. No. 4,656,921 (hydraulic fluid), U.S. Pat. No. 4,972,760 (adjustable recoil spring), U.S. Pat. No. 5,353,681 (recoil spring, friction, and pneumatics), and U.S. Pat. No. 5,617,664 (recoil spring).
In the particular case of some explosives disrupter devices for de-arming explosives devices, there may be no recoil mitigation. Disrupter devices are typically attached to a support frame mounted on the ground or mounted on a remote-controlled robot whereby the device can be triggered from a relatively safe distance to fire a projectile into an article suspected of containing a bomb or other explosive. Such devices are generally of a single-shot design and produce a significant impulse—oftentimes sufficient to propel the support frame/robot backwards, cause it to topple over, and/or sustain significant damage. Depending upon the situation, such devices may be called upon to fire a variety of projectiles at a variety of velocities from a variety of support frame/robots. This in turn creates a variety of recoil forces requiring, in turn, a variety of recoil mitigation solutions tailored to each support frame/robot. For example, the momentum imparted to the device from a column of water, often used to disarm soft-package bombs such as suspected briefcase bombs, may vary from close to 5 pounds-force-seconds at a low velocity to over 9 pounds-force-seconds at a high velocity (140 milliliter load at a velocity of 1000 feet per second) and even as high as 12 pounds-force-seconds. Metal slugs impart momentum in the range of 4 pounds-force-seconds to 6 pounds-force-seconds.
A general rule of thumb for a weapon without recoil mitigation fired by a human is that the momentum should not exceed 3 pounds-force-seconds. By comparison, the momentum carried by a 150 grain projectile fired from a 30-06 rifle at a velocity of 2810 feet per second is approximately 1.87 pounds-force-seconds. Thus, the momentum generated by an explosives disrupter can be relatively significant.
Therefore, there is a need for a recoil-mitigation device which overcomes these disadvantages.